It is known to hydroform tubular components. Hydroformed tubular components are becoming increasingly popular in automotive body structural applications. Moreover, curved hydroformed tubular components are used for some of these applications. In general, curved hydroformed tubular components require bent pre-forms before going to the final hydroforming dies for final part shapes. To make good final parts, usually good bent pre-forms are required, which are free of splits or deep wrinkles.
Conventional methods for bending a tube usually employ rotary draw bending machines with a set of bend dies, a mandrel, and other tools. The bent tubes from those bending machines usually have circular cross-sections along the whole length and free of split and deep wrinkles.
Using this traditional practice, there are some limitations regarding a ratio between bend radius (R) and tube diameter (D) of the tube to be acceptable for subsequent hydroforming operation (R/D>2). For lower ductility materials such as high-strength steel and aluminum, the ratio should be larger. In some applications, this limitation on using larger bend radius could restrict some hydroform applications that require tight-bend design features or using alternative light-weight materials.
Another potential problem with a bent tube is wrinkle on its compressive surface, especially for thin gage tube or tightly bent tube. Some of these wrinkles could be flattened out by high pressure used in the hydroforming process, but not for somewhat deep wrinkles. The common practice is to use a wrinkle-free pre-form to ensure successful subsequent hydroforming operation.
As a result, it is desirable to provide a method of making curved hydroformed tubular members. It is also desirable to provide a method of pre-forming tubular members that improves hydroforming formability for a wider range of hydroforming applications. It is further desirable to provide a method of pre-forming tubular members that minimizes thinning and avoids splitting during a bending process. Therefore, there is a need in the art to provide a method of making pre-formed tubular members that meets these desires.